1. Field of the Invention
The present invention relates to an anti-reflective polymer that is useful in a submicrolithographic process, a composition comprising the polymer, and a method for preparing the same. In particular, the present invention relates to a polymer that can be used in an anti-reflective coating layer to reduce or prevent back reflection of light and/or to eliminate the standing waves in the photoresist layer during a submicrolithographic process. The present invention also relates to a composition comprising the polymer, and a method for using the same.
2. Description of the Prior Art
In most submicrolithographic processes standing waves and/or reflective notching of the waves typically occur due to the optical properties of the lower layer coated on a substrate and/or due to changes in the thickness of a photosensitive (i.e., photoresist) film applied thereon. In addition, typical submicrolithographic processes suffer from a problem of CD (critical dimension) alteration caused by diffracted and/or reflected light from the lower layer.
One possible solution is to apply an anti-reflective coating (i.e., ARC) between the substrate and the photosensitive film. Useful ARCs have a high absorbance of the light wavelengths that are used in submicrolithographic processes. ARCs can be an inorganic an organic material, and they are generally classified as xe2x80x9cabsorptivexe2x80x9d or xe2x80x9cinterferingxe2x80x9d depending on the mechanism. For a microlithographic process using I-line (365 nm wavelength) radiation, inorganic anti-reflective films are generally used. Typically, TiN or amorphous carbon (amorphous-C) materials are used for an absorptive ARC and SiON materials are typically used for an interfering ARC.
SiON-based anti-reflective films have also been adapted for submicrolithographic processes that use a KrF light source. Recently, use of an organic compound as ARC has been investigated. It is generally believed that an organic compound based ARCs are particularly useful in submicrolithographic processes, in particular those using an ArF light source.
In order to be useful as an ARC, an organic compound needs to have many diverse and desirable physical properties. For example, a cured ARC should not be soluble in solvents because dissolution of the organic ARC can cause the photoresist composition layer to peel-off in a lithographic process. One method for reducing the solubility of cured ARC is to include cross-linking moieties such that when cured the ARC becomes cross-linked and becomes insoluble in most solvents used in lithographic processes. In addition, there should be minimum amount of migration (i.e., diffusion), if at all, of materials, such as acids and/or amines, to and from the ARC. If acids migrate from the ARC to an unexposed area of the positive photoresist film, the photosensitive pattern is undercut. If bases, such as amines, diffuse from the ARC to an unexposed area of the positive photoresist film a footing phenomenon occurs. Moreover, ARC should have a faster etching rate than the upper photosensitive (i.e., photoresist) film to allow the etching process to be conducted smoothly with the photosensitive film serving as a mask. Preferably, an organic ARC should be as thin as possible and have an excellent light reflection prevention property.
While a variety of ARC materials are currently available, none of these materials is useful in ArF laser submicrolithographic processes. In the absence of an ARC, the irradiated light penetrates into the photoresist film and is back reflected or scattered from its lower layers or the surface of the substrate (e.g., semiconductor chip), which affects the resolution and/or the formation of a photoresist pattern.
Therefore, there is a need for an ARC material which have a high absorbance of the wavelengths used in submicrolithographic processes.
It is an object of the present invention to provide an organic polymer that can be used as an ARC material in ArF laser (193 nm) or KrF laser (248 nm) submicrolithographic processes.
It is another object of the present invention to provide a method for preparing an organic polymer that reduces or prevents diffusion and/or light reflection in submicrolithographic processes.
It is a further object of the present invention to provide an ARC composition comprising such an organic diffusion/reflection preventing or reducing polymer and a method for producing the same.
It is a still further object of the present invention to provide a method for producing a photoresist pattern using ArF laser submicrolithographic processes with reduced standing wave effect.
It is yet another object of the present invention to provide a semiconductor device which is produced using the ARC composition in a submicrolithographic process.
One aspect of the present invention provides an acrylate polymer, an ARC composition comprising the same, and a method for using the same. In one particular embodiment, the polymer of the present invention comprises a chromophore which has a high absorbance of light wavelengths of 193 nm and 248 nm.
ARC compositions of the present invention can comprise a mixture polymers which include cross-linking moieties such that the polymers become cross-linked when heated (i.e., cured or xe2x80x9chard bakedxe2x80x9d). Cross-linking moieties can comprise an alcohol group and other functional group that is capable of reacting with the alcohol group to form a cross-linkage. It is believed that cross-linking of the polymer significantly improves the adhesiveness and the dissolution properties of ARC compositions.
Uncured polymers of the present invention are soluble in most hydrocarbon solvents; however, cured polymers are substantially insoluble in most solvents. Thus, polymers of the present invention can be easily coated onto a substrate and are capable of preventing undercutting and footing problems that can occur during a photoresist pattern formation process on photosensitive materials (i.e., photoresist compositions). Moreover, ARCs of the present invention have a higher etching rate than conventional photosensitive films resulting in an improved etching ratio between ARCs and photosensitive films, i.e., higher etching selectivity.
One embodiment of the present invention provides an ARC polymer selected from the group consisting of a polymer of the formula: 
wherein
each of R12, Ra, Rb, and Rc is independently hydrogen or optionally substituted C1-C10 alkyl, preferably hydrogen or methyl;
each of R1 to R9 is independently hydrogen, optionally substituted C1-C5 alkyl, or optionally substituted C1-C5 alkoxyalkyl;
Rd, R10 and R11 are independently optionally substituted C1-C10 alkyl;
x, y and z are mole fractions, each of which is independently in the range of from about 0.01 to about 0.99;
each of m and n is independently an integer of 1 to 5.
Alkyl groups according to the present invention are aliphatic hydrocarbons which can be straight or branched chain groups. Alkyl groups optionally can be substituted with one or more substituents, such as a halogen, alkenyl, alkynyl, aryl, hydroxy, amino, thio, alkoxy, carboxy, oxo or cycloalkyl. There may be optionally inserted along the alkyl group one or more oxygen, sulfur or substituted or unsubstituted nitrogen atoms. Exemplary alkyl groups include methyl, ethyl, i-propyl, n-butyl, t-butyl, fluoromethyl, difluoromethyl, trifluoromethyl, chloromethyl, trichloromethyl, and pentafluoroethyl.
Particularly useful polymers of Formula 3 include the following polymers: 
Polymers of Formulas 4 to 7 can be cured by contacting with an alcohol-containing compound in the presence of an acid.
Another aspect of the present invention provides a method for producing polymers disclosed above.
Polymers of Formula 1 can be produced by polymerizing a mixture of monomers comprising a 9-anthracenealkylacrylate monomer of the formula: 
and a hydroxyalkylacrylate monomer of the formula: 
under conditions sufficient to produce the polymer of Formula 1, where Ra, Rb, R1 to R9, and n are those defined above. Each monomer in the mixture has a mole fraction ranging from 0.01 to 0.99.
Polymers of Formula 2 can be produced by polymerizing a mixture of monomers comprising a 9-anthracenealkyl acrylate monomer of Formula IA above, a hydroxy alkylacrylate monomer of Formula IB above, and an alkylacrylate monomer of the formula: 
under conditions sufficient to produce the polymer of Formula 2, where Rc and Rd are those defined above. Each monomer in the mixture has a mole fraction ranging from 0.01 to 0.99.
The hydroxy alkylacrylate monomer of Formula IB and the alkylacrylate monomer of Formula IC are commercially available or can be readily prepared by those skilled in the art.
Polymers of Formula 3 can be produce by polymerizing an acrolein monomer of the formula: 
under conditions sufficient to produce a poly(acrolein) polymer of the formula: 
and reacting the poly(acrolein) polymer of Formula IE with an alcohol under conditions sufficient to produce the poly(acetal) polymer of Formula 3. The alcohol can be a mixture of different alcohols (e.g., R10xe2x80x94OH and R11xe2x80x94OH, where R10 and R11 are those defined above) or a homogeneous alcohol system (i.e., only one type of alcohol is present). For example, a solution of (meth)acrolein in an organic solvent is polymerized at 60-70xc2x0 C. for 4-6 hours under vacuum in the presence of a polymerization initiator, after which the resulting polymeric product is reacted with C1-C10 alkyl alcohol at room temperature for 20-30 hours in the presence of an acid catalyst, e.g., trifluoromethylsulfonic acid. Examples useful alcohols include C1-C10 alkyl alcohols such as methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, and isomers thereof. In particular, methanol and ethanol are preferred.
The polymerization reactions disclosed above can include a polymerization initiator. Suitable polymerization initiators are well known to one of ordinary skill in the art including polymerization initiators that are used in conventional radical polymerization reactions such as 2,2-azobisisobutyronitrile (AIBN), benzoylperoxide, acetylperoxide, laurylperoxide, t-butylperacetate, t-butylhydroperoxide, and di-t-butylperoxide.
The polymerization reactions disclosed above can also include a polymerization solvent. Suitable polymerization solvents are well known to one of ordinary skill in the art. Exemplary polymerization solvents include organic solvents that are used in conventional polymerization reaction. Preferably, the polymerization solvent is selected from the group consisting of tetrahydrofuran (THF), cyclohexanone, dimethylformamide, dimethylsulfoxide, dioxane, methylethyl ketone, benzene, toluene, xylene and mixtures thereof.
Another aspect of the present invention provides an ARC composition comprising a cross-linked polymer produced from cross-linking a polymer of Formula 3 with a polymer of Formula 1 or 2, or mixtures thereof. The cross-linked polymer can be produced by admixing a polymer of Formula 3 and a polymer of Formula 1 or 2, or mixtures thereof under conditions sufficient to produce the cross-linked polymer. Typically, this cross-linking reaction is conducted in a conventional organic solvent. Suitable organic solvents for a cross-linking reaction are well known to one skilled in the art and include, but are not limited to, ethyl 3-ethoxypropionate, methyl 3-methoxypropionate, cyclohexanone, and propylene glycol methyletheracetate. The amount of solvent used is preferably from about 200 to about 5,000% by weight of the total weight of the polymer.
The ARC composition of the present invention can also include one or more anthracene derivative additives. Exemplary anthracene derivative additives include, but are not limited to, anthracene, 9-anthracenemethanol, 9-anthracenecarbonitrile, 9-anthracenecarboxylic acid, dithranol, 1,2,10-anthracenetriol, anthraflavonic acid, 9-anthraldehydeoxime, 9-anthraldehyde, 2-amino-7-methyl-5-oxo-5H-[1]benzopyrono[2,3 -b]benzopyridine-3-carbonitrile, 1-aminoanthraquinone, anthraquinone-2-carboxylic acid, 1,5-dihydroxyanthraquinone, anthrone, 9-anthryltrifluoromethyl ketone, 9-alkylanthracene derivatives of the formula: 
carboxylanthracene derivatives of the formula: 
and carboxylanthracene derivatives of the formula: 
where each of R13, R14, and R15 is independently hydrogen, hydroxy, optionally substituted C1-C5 alkyl, or optionally substituted C1-C5 alkoxyalkyl.
Another aspect of the present invention provides a method for producing an ARC coated substrate. In one particular embodiment, a substrate (e.g., wafter) is coated with an anti-reflective coating composition comprising a mixture of polymers. The mixture of polymers comprises a polymer of Formula 3 and a polymer of Formula 1 or 2, or mixtures thereof. The mixture of polymers can be dissolved in an organic solvent and filtered prior to being coated. The mixture of polymers can also include one or more additives described above. The coated substrate is then heated (i.e., hard-baked) to produce the ARC coated substrate. Preferably the coated substrate is heated to temperature in the range of from about 100 to about 300xc2x0 C. for a period of from about 10 sec to about 1,000 sec. Heating the substrate causes cross-linking of the polymers to produce a thin film of ARC coating.
It has been found by the present inventors that the ARCs of the present invention exhibit high performance in submicrolithographic processes, in particular using KrF (248 nm), ArF (193 nm) and F2 (157 nm) lasers as alight source.
Additional objects, advantages, and novel features of this invention will become apparent to those skilled in the art upon examination of the following examples thereof, which are not intended to be limiting.